The invention relates to the storage of banknotes or other sheets of value, which are herein referred to simply as banknotes.
It is known hereto to provide a banknote store comprising first and second drums with a strip wound onto both drums and arranged to support banknotes disposed in succession between windings of the strip on the first drum. The strip is wound from the first drum to the second drum to expose successive supported banknotes for removal and is wound from the second drum to the first drum to enable banknotes to be deposited successively on the first drum. The second drum is driven to rotate to wind the strip from the first to the second drum while the first drum may be driven to follow the second drum. In the opposite direction, the first drum is driven to rotate to wind the strip from the second to the first drum while the second drum may be driven to follow the first drum. It is known for the first and the second drums to be fixed for rotation relative to respective shafts which are themselves driven by one or more motors.
When the strip is wound from one to the other drum, it important for the strip to be held firmly between the two drums at all times. As banknotes are stored in discrete locations relative to the strip, movement of the strip would mean that the control arrangement of the banknote store would not be able to locate the exact position of individual banknotes.
During operation, as the number of windings decreases on one drum, the length of strip unwound therefrom also decreases, provided the rotational speed of the drum remains constant. The same is true in reverse. That is, as the number of windings on the other drum increases, the length of strip being wound onto the other drum increases, again, provided the rotational speed of the drum remains constant. This is because the length of strip wound onto or unwound from a drum is dependent on the circumference of the outer winding on the drum. In the prior art, the strip may be held firmly between the drums, by winding the strip onto one drum by rotating that drum, whilst providing some resistance to rotation of the other drum, from which the strip is being unwound. This arrangement enables the strip to be held firmly only when the drums are rotating but may not when the drums are stationary.
In an alternative prior art arrangement, the drums are rotated at varying speeds. In this way, as the strip is unwound from one drum, the drum may be rotated gradually more quickly, because the length of strip being unwound from it per revolution gradually decreases. The reverse is true for the other drum, which may be rotated gradually more slowly as the length of strip being wound onto it per revolution gradually increases. The continuous adjustment of the rotational speeds of the drums requires relatively complicated and expensive arrangements and control of the motor or motors driving the shafts.
It is known that as the diameter of the banknote store increases, the stability of the store decreases, and it may interfere with other components of the apparatus. In the prior art, this problem was solved by limiting the number of banknotes that could be stored.
U.S. Pat. No. 6,715,753 discloses a method directed to this problem which involves a belt tightening operation to increase the storage capacity. One feature of the method is determination of the radius of a spool on a driven reel, which is used to ensure that the storage belt has the same speed at all times. The radius is determined as the ratio of velocity of the belt from a belt speed measuring sensor and the angular velocity from a stepping motor for the driven reel.